The invention relates to a device for compensating the weight of a robot arm of a robot with a spring cylinder or housing having at least one helical spring, as well as a robot equipped with such a device.
For the compensation of static loads a robot generally has at least one weight compensating device, which is e.g. constructed as a spring cylinder or fluid spring, particularly a gas spring. In the case of multiaxial industrial robots, which have a carrousel pivotable about a base axis (A1-axis) located on a frame and a robot arm pivotable about several axes and located on a rocker arm on the carrousel, such devices are more particularly provided between the rocker arm and the carrousel in order to absorb the load moments of the A2-axis. They are e.g. fixed in such a way to the rocker arm or robot arm, that they are compressed or extended on deflecting the rocker arm or robot arm and consequently transform the pressure dependent on robot arm deflection into a force dependent on said deflection for compensating the gravity or the torque caused by it exerted on the rocker arm or robot arm.
When using gas springs it is disadvantageous that the relationship between the deflection and force of the gas spring is only proportional for as long as the behaviour of the gas approximately corresponds to the ideal gas equation. Since in particular at higher gas pressures, the gas no longer behaves in an ideal manner and is heated on compression and cools on depression and conversely the gas pressure also changes with temperature fluctuations, the force produced by gas springs has a considerable fluctuation range, which leads to a fluctuating load compensation due to temperature changes, which must be compensated by regulating and control processes. Leaks in the gas springs also lead to a failure of the weight compensation, so that monitoring devices respond, followed by the disconnection of the robot and plant shutdown, which can result in robot overload and damage.
The disadvantage of spring cylinders or housings is in particular that they have a substantially invariable spring constant and can consequently not be used in flexible manner. If different demands are made on the compensating force of a robot weight compensation, either when changing to a different carrying capacity or when changing the motion ratios of the robot, the spring cylinder must be replaced, which is complicated and costly and makes it necessary to stock several spring cylinders with different spring constants. Therefore the problem of the invention is to so further develop a device for compensating the weight of a robot arm of a robot with a spring cylinder having at least one helical spring in such a way that it can be adapted to the compensation forces necessary for the motion ratios and load states of the robot and can consequently also be flexibly used with varying load ratios and different robots.
According to the invention this problem is solved in the case of a device of the aforementioned type by at least one mechanism for the easy insertion and removal of at least one further, replaceable helical spring of the spring cylinder.
As a result of the construction according to the invention the weight compensating device is universally usable, in that as a function of the necessary compensating force of the weight compensation the replaceable helical spring is removed or helical springs with different spring constants are inserted in the spring cylinder. In place of the entire spring cylinder it is only necessary to insert, remove or replace the interchangeable helical springs. In particular there is no need to dismantle the spring cylinder from the robot and instead the robot arm having the weight compensation is e.g. secured and the helical spring is replaced on the fitted spring cylinder. The weight compensating device according to the invention is consequently suitable for different robots with different motion ratios and load states and makes it unnecessary to store spring cylinders with different spring constants.
What is important is the usability and replaceability of the additional helical springs without dismantling or disconnection of the spring cylinder from the robot. Thus, in its working cell or location a robot can be easily converted to other carrying capacities, which leads to a considerable time saving compared with existing possibilities.
Whilst the spring cylinder can fundamentally have a fixed installed helical spring, in a preferred construction it has two of these and also a replaceable helical spring, so that both the fixed installed helical springs and also the replaceable helical spring contribute to the overall spring constant of the weight compensation. If the fixed installed and replaceable helical springs are arranged in parallel, the total spring constant of the spring cylinder is the sum of the spring constants of the fixed installed and replaceable helical springs. It is obviously possible to provide more than two fixed installed helical springs and more than one replaceable helical spring, which are connected in parallel for obtaining a high spring constant.
For compactness reasons the helical springs are preferably arranged substantially concentrically, the replaceable helical spring preferably being positioned centrally. To permit easily insertion and removal of the replaceable helical spring, in this case it is preferable to place on an end face of the spring cylinder facing a bottom forming an abutment for the helical springs, a lid with a central bore or hole for the replacement of the replaceable helical spring. The hole preferably has a cover, through which in particular a contact protection is provided, but which can also form a substantially dust-tight and moisture-tight closure.
In another preferred construction, an inner disk forming an abutment for the replaceable helical spring and connected to a piston rod of the spring cylinder as provided and which is detachably connected to an outer disk forming an abutment for the fixed installed helical springs. In particular, the external diameter of the outer disk is larger and the external diameter of the inner disk smaller than the diameter of the central hole in the spring cylinder lid. Thus, for replacing the replaceable helical spring the inner disk can be detached from the outer disk and removed together with the replaceable helical spring through the hole in the spring cylinder lid, whilst the outer disk, as a result of its diameter exceeding the hole diameter, retains in the spring cylinder the fixed installed helical springs.
According to a preferred construction, a pretensioning of at least the replaceable helical spring is adjustable, so as to vary the desired total spring constant of the spring cylinder. For this purpose is provided a spindle on the spring cylinder piston rod for adjusting the replaceable helical spring length corresponding to the desired pretension and on which is axially displaceably fixed in particular an abutment for the inner disk forming the replaceable helical spring, e.g. by means of a nut.
Preference is also given to an adjustability of a pretension of at least one further, fixed installed helical spring, the length of the fixed installed helical spring corresponding to the desired pretension being e.g. adjustable together with the length of the replaceable helical spring corresponding to the desired pretension using the spindle, which can in particular be ensured by the detachable connection between the inner and outer disks.
In order to ensure an easy and reliable replacement of a replaceable helical spring to be inserted in the spring cylinder and having a length exceeding that corresponding to the desired pretension, according to a preferred construction a mounting spindle placeable on the piston rod of the spring cylinder is provided for compressing such a replaceable helical spring during insertion in the spring cylinder. Preferably the mounting spindle can be placed on the end face of the spindle remote from the spring cylinder in a coaxial and aligned manner, so that in particular on fitting a replaceable helical spring the inner disk is placed and fixed by means of the mounting spindle on the spring cylinder spindle.
In order to ensure a completely satisfactory operation of the device according to the invention, preferably centering devices are provided for the concentric arrangement of the helical springs in the spring cylinder and on the one hand there is a centering cylinder at least concentrically guiding the replaceable helical spring with respect to an adjacent, fixed installed helical spring and preventing a contact between the replaceable helical spring and the adjacent, fixed installed helical spring, and on the other a centering ring concentrically guiding at least an inner with respect to an outer, fixed installed helical spring. The inner disk preferably also has a centering shoulder engaging in the replaceable helical spring and, if there are at least two fixed installed helical springs, the outer dial has a centering collar concentrically guiding an inner with respect to an outer, fixed installed helical spring.
The invention also relates to a robot, particularly a multiaxial industrial robot, which is equipped with such a weight compensating device.